1. Field of the Invention
This invention relates to a projector that projects and displays images.
2. Description of the Related Art
A projector usually comprises an illuminating optical system and liquid crystal panels for modulating light from the illuminating optical system responsive to image information (an image signal). The modulated light is then projected onto a screen by a projection lens.
FIG. 10 is an explanatory diagram showing the main part of a conventional projector. This projector comprises three liquid crystal light valves 900R, 900G and 900B, a cross-dichroic prism 920 and a projection lens 940. Colored light of the three colors red (R), green (G) and blue (B) emitted from an illuminating optical system (not shown) is caused to pass through the liquid crystal light valves 900R, 900G and 900B and thus modulated responsive to image information. The modulated light (modulated light beams) is combined by the cross-dichroic prism 920 and the composite light is projected by the projection lens 940. A color image is thus displayed upon the screen SC. Note that in FIG. 10, it is assumed that s-polarized colored light R, G and B is incident upon the liquid crystal light valves 900R, 900G and 900B.
The second liquid crystal light valve 900G comprises a liquid crystal panel 901G and polarizing plates 902Gi and 902Go at the incident and exit sides of the liquid crystal panel 901G, respectively. The polarization axes of the polarizing plates 902Gi and 902Go are set at right angles with each other. The incident side plate 902Gi transmits s-polarized light whereas the exit side plate 902Go transmits p-polarized light. With such a configuration, the s-polarized light incident on the second liquid crystal light valve 900G is converted to p-polarized light and then emitted.
The first liquid crystal light valve 900R comprises a liquid crystal panel 901R, a p-polarized light transmitting polarizing plate 902Ri, an s-polarized light transmitting polarizing plate 902Ro, and a xcex/2 retardation plate 903R. The xcex/2 retardation plate 903R is affixed to a glass plate 908, and the first polarizing plate 902Ri is affixed to the xcex/2 retardation plate 903R. The s-polarized light incident on the glass plate 908 is converted to p-polarized light by the xcex/2 retardation plate 903R, is transmitted through the p-polarized light transmitting polarizing plate 902Ri and is then converted to s-polarized light by the liquid crystal panel 901R and the s-polarized light transmitting polarizing plate 902Ro and emitted. The third liquid crystal light valve 900B has the same structure as the first light valve 900R.
The dichroic films of the cross-dichroic prism reflect s-polarized light more effectively than p-polarized light, and transmit p-polarized light more effectively than s-polarized light. Thus, the s-polarized light emitted from the first and third liquid crystal light valves 900R and 900B and the p-polarized light emitted from the second liquid crystal light valve 900G can be efficiently combined by the cross-dichroic prism 920.
In this Specification, the term xe2x80x9cliquid crystal light valvexe2x80x9d denotes a liquid crystal light valve in the broad sense, and it refers to a unit that comprises at least a liquid crystal panel and polarizing plates, and that may further comprises a xcex/2 retardation plate. Note that a liquid crystal light valve in the narrow sense refers to a unit that includes a liquid crystal panel and polarizing plates and that does not include a xcex/2 retardation plate.
The light illuminating the polarizing plate of the liquid crystal light valve generates heat to cause distortion of the polarizing plate occurs. Note that the amount of this distortion depends mainly on the intensity and distribution of the light which illuminates the polarizing plate.
In the aforementioned conventional projectors, the xcex/2 retardation plates 903R and 903B contained in the first and third liquid crystal light valves 900R and 900B are sandwiched between the glass plate 908 and the polarizing plates 902Ri and 902Bi. For this reason, the distortion of the polarizing plate 902Ri causes distortion of the xcex/2 retardation plate 903R.
FIG. 11 is a plan view of the polarizing plate 902Ri provided on the incident side of the first liquid crystal light valve 901R shown in FIG. 10 when viewed from the xe2x88x92x direction. Note that in the direction going back into the plane of the paper (the +x direction) from the polarizing plate 902Ri, the xcex/2 retardation plate 903R and the glass plate 908 are disposed in this order. As shown by the broken lines in the figure, the heating of the polarizing plate 902Ri is normally relatively large near the center and relatively small in the periphery. In this case, the polarizing plate 902Ri becomes distorted in the directions indicated by arrows. At this time, when the polarizing plate 902Ri becomes distorted, the xcex/2 retardation plate 903R sandwiched between the polarizing plate 902Ri and glass plate 908 also become distorted in the directions indicated by arrows. This phenomenon can occur in the same manner even in the case wherein the intensity distribution of the light beams illuminating the liquid crystal light valves is relatively uniform.
In the case wherein the xcex/2 retardation plate 903R is distorted in this manner, the distorted portions of the xcex/2 retardation plate 903R (FIG. 10) cannot efficiently convert the incident s-polarized light into p-polarized light. Thus, the intensity of the p-polarized light emitted from the p-polarized light transmitting polarizing plate 902Ri on the incident light becomes lower, and so does the intensity of s-polarized light emitted from the spolarized light transmitting polarizing plate 902Ro on the exit side. In this manner, nonuniformities occur in the brightness of the modulated light beam emitted from the liquid crystal light valve 900R. When such a modulated light beam is used to display a color image on the screen SC, chrominance nonuniformities occur within the displayed image.
An object of the present invention is thus to provide a technique for reducing chrominance nonuniformities in the images displayed by a projector.
At least part of the above and other objects of the present invention is attained by a projector for projecting and displaying a color image. The first projector comprises: an illuminating optical system that emits illuminating light; a color-separating optical system that separates the illuminating light emitted from the illuminating optical system into a first through third beam of colored light, each of which has one of three color components; first through third electro-optical devices that modulate the first through third beams of colored light separated by the color-separating optical system according to image information to form a first through third beam of modulated light; a color combiner that combines the first through third beams of modulated light by reflecting the first and third beams of modulated light while transmitting the second beam of modulated light; a projecting optical system that projects the composite light emitted from the color combiner; and a xcex/2 retardation plate provided on at least one of an incident side and an exit side of both of the first and third electro-optical devices, the xcex/2 retardation plate having a first surface open to the atmosphere and a second surface in contact with a transmissive member.
Since the xcex/2 retardation plate is provided with one surface open to the atmosphere and its other surface in contact with a transmissive member, the distortion of the xcex/2 retardation plate is reduced, and the chrominance nonuniformities in the images displayed are reduced accordingly.
In a preferred embodiment of the invention, a direction of polarization of the first and third beams of modulated light incident on the color combiner is a first direction of polarization, while a direction of polarization of the second beam of modulated light is a second direction of polarization perpendicular to the first direction.
In this arrangement, the color combiner can combine the first through third beams of modulated light effectively.
In a preferred embodiment of the invention, the illuminating optical system comprises: a polarized light generator for emitting the illuminating light as linearly polarized light having the first or second direction of polarization.
In this arrangement, the light incident on the first through third electro-optical devices has a uniform direction of polarization, and the light can be utilized effectively.
In a preferred embodiment of the invention, the xcex/2 retardation plate is affixed to one surface of the transmissive member, and the electro-optical device includes a polarizing plate affixed to another surface of the transmissive member.
Although the xcex/2 retardation plate and polarizing plate are provided on the same transmissive member in this arrangement, the distortion of the xcex/2 retardation plate is reduced by the above stated mechanism and the chrominance nonuniformities are reduced in the images displayed.
In a preferred embodiment of the invention, the xcex/2 retardation plate is affixed to one surface of the transmissive member, and the electro-optical device includes a polarizing plate affixed to a second transmissive member other than the transmissive member to which the xcex/2 retardation plate is affixed.
In this arrangement also, the distortion of the xcex/2 retardation plate is also reduced, and the chrominance nonuniformities are reduced in the images displayed.
Alternatively, the second projector comprises: an illuminating optical system that emits illuminating light; a color-separating optical system that separates the illuminating light emitted from the illuminating optical system into a first through third beam of colored light, each of which has one of three color components; first through third electro-optical devices that modulate the first through third beams of colored light separated by the color-separating optical system according to image information to form a first through third beam of modulated light; a color combiner that combines the first through third beams of modulated light by reflecting the first and third beams of modulated light while transmitting the second beam of modulated light; a projecting optical system that projects the composite light emitted from the color combiner; and a xcex/2 retardation plate provided on at least one of an incident side and an exit side of the second electro-optical device, the xcex/2 retardation plate having a first surface open to the atmosphere and a second surface in contact with a transmissive member.
This second projector has same function and advantage as the above first projector.